1. Field of the Invention
The present invention relates generally to an electro-optic polymer waveguide device capable of decreasing a driving voltage and an optical loss and a method of manufacturing such an electro-optic polymer waveguide device.
2. Description of Related Art
Since a waveguide device using a polymer can be applied to a variety of application field and be mass-produced of low price, it has been lively studied recently.
The polymer waveguide device can be divided into a passive type polymer and a nonlinear type polymer. The passive type polymer can be applied to an optical power distributor or a thermo-optic switch, including a device using thermo-optic effects.
L. Eldada et al. (IEEE J. Lightwave Technol., Vol. 14, No. 7, pp. 1704-1713, July 1996) has developed material capable of decreasing an optical propagation loss of a polymer waveguide under 0.1 dB/cm. Akzo company has produced and sold commercially a thermo-optic switch having a high stability and low driving voltage.
Study of the nonlinear type polymer has been progressed in a direction using electro-optic effects. Recently, W. H. Steier et al. has published an optical modulator having a band of modulation frequency over 100 GHz in a title "High bandwidth polymer modulators in Optoelectronic Integrated Circuits", Proc. SPIE 3006, pp. 314-317, 1997.
Mach-Zehnder modulator using the electro-optic polymer waveguide has an advantage of low velocity mismatch between a lightwave and a microwave, thereby easily making an optic device having a broad bandwidth of modulation.
In spite of such an advantage, since the electro-optic polymer waveguide device has not been still optimized completely in various characteristics, it is not enough as an practical application device.
The electro-optic polymer waveguide has advantage of allowing high-speed signal process over 100 GHz, but has the shortage of a large light-insertion loss and a large driving voltage, thereby having limitation in the practical application.
To reduce the driving voltage of the electro-optic waveguide device, it is required to decrease the thickness of the electro-optic waveguide device so as to minimize a distance between modulating electrode. For this, it is required to make a large difference of refractive index between a core layer and a cladding layer to limit waveguide light to the very thin core layer. Further, it is required to make a whole thickness of the waveguide enough thin by making the thicknesses of the upper and lower cladding layers very thin.
Since the driving voltage is applied between two electrodes sandwitching the waveguide, the thickness of the waveguide is thinner, the electric field is larger, whereby an efficiency of the optical modulation using the electro-optic effects is increase and the driving voltage of the device is lowered.
If the thickness of the waveguide is made thinnest, the driving voltage is minimized, but since an amplitude of waveguide light becomes too small as compared with that of the optical fiber mode, loss due to mode mismatch is too large during input and output between the optical fiber and the device. Moreover an allowable error at the time of aligning with the optical fiber is too small.